The present invention relates to position sensors and more particularly to housings for position sensors for mounting the position sensor onto testing equipment or associated devices.
In one embodiment, a sensor with an outer flange is used in conjunction with an outer body (sensor housing) having an inner flange to provide a definite position for the sensor, which position is repeatable on the re-installation of the original sensor or the placement of a substitute sensor into the housing. In another embodiment, the housing includes pre-loaded sprung balls that are positioned and biased to push radially inwardly against a radially outwardly facing, circumferential groove formed on the sensor to provide a radially inwardly, and axially downwardly directed force on the sensor to assure good registry to the flanges of both the sensor and outer housing, thereby maintaining a repeatable position of the sensor.
Sensors are often placed within equipment, tooling, gauge fixtures and the like to help determine the size and shape characteristics of a workpiece, such as an automotive component (e.g. an automobile windshield or other glass member that is placed on the tooling fixture or the like. Many of these sensors are linear displacement-type sensors having a tubular construction, or at least have a partially tubular design in that portion of the sensor (the distal end) that is nearer to the sensor tip. Traditionally these sensors have been attached to fixtures through clamping, set screw and ball detents. Clamping and set screw attachment mechanisms have significant problems when used with many of the mechanical and electronic sensors used in today""s equipment and products, because such attachment mechanisms can exert sufficient force on the sensor to pinch or distort the sensor, thereby causing inaccurate readings or else making the movable member of the sensor inoperable due to seizure or unreliable due to increased frictional resistance to the movement of the movable member caused by the pending forces of the attachment means. Seizure of the sensor occurs when the clamping mechanism that holds the sensor exerts a force on the movable member of the sensor, thereby impeding or preventing the movement of the movable sensor member. Clamping also has the draw back of requiring a tool, such as a wrench or Allen key to remove the sensor from the housing.
Prior known ball detent mechanisms, although allowing quick removal of the sensor, have not provided a sufficiently sturdy grip on the sensor to assure that the sensor is maintained in a consistent and accurate location. Bolting the sensor in place provides a good attachment but provides for slow removal of the sensor for service or replacement. Few if any commercially available linear sensors are provided in a condition ready for attachment by use of a bolting means.
Within the automotive component fixture industry, the common practice is to clamp sensors into position by utilizing a circumferential clamping system, that functions similarly to a hose clamp. These circumferential clamping systems can have a strong holding force, but apply an inordinate amount of radially directed load on the sensor, thereby often distorting the housing, and thereby impeding the movement of the movable portion of the sensor, which results in decreasing the performance and/or life span of the sensor. Distortion of the housing can impair the sensor""s performance by binding the movable plunger element of the sensor, or otherwise retarding its movement.
However, attempting to eliminate this binding force by reducing this clamping force creates its own problems. In particular, if the clamping force exerted on the sensor is reduced to a point that permits normal, non-bound or non-distorted operation of the sensor plunger, the sensor winds up being held too weakly by the clamp to be held in a stable, unmoving position thereby.
As can be deduced from this discussion, room exists for improving upon the prior art sensors. Specifically, a need exists for a sensor placement system: (1) that allows quick removal and replacement of the sensor for service; (2) that has the ability to hold the sensor firm and stable while operating; and (3) that is capable of achieving an accurate and repeatable positioning of the sensor when the sensor(s) in the fixture, tool or equipment are replaced. One object of the present invention is to provide such a device.
In accordance with the present invention, an attachment system is provided for a sensor system that permits a linear sensor to be removed and replaced quickly without the need for tools; secures the sensor firmly in a manner that eliminates movement between the housing and the sensor; and provides a system by which replacement sensors can be positioned accurately with repeatability.
Preferably, each of the sensor and the housing include a mating flange that creates a pair of mating surfaces for providing a consistent matching plane of engagement. The seating of the sensor flange on the housing flange allows for repeatability of the insertion depth of the sensor into the housing. The flange also helps achieve accuracy in the depth that the sensor is inserted into the housing. The flange further provides an area of contact in a plane perpendicular to the axis of insertion, thereby enhancing the stability and firmness with which the sensor is held in the housing. The mating flanges can be continuous, circumferential flanges or a segmented, circumferential flanges having sections removed to permit insertion of the sensor from the rear or front of the housing, while still holding the sensor securely in position when assembled. The mating surfaces of the mating flanges can also be tangential to the circumference of the face of the flange; or alternately, the mating surfaces can be perpendicular to the axis of the insertion or measuring axis.
Alternately, the attachment housing can use a holding system that consists of a clamp, set screw, ball detents, groove and clamp, bolts, or other common system of holding fast tubular structures within a tube. It is preferable that the holding system applies a load in an axial direction to pull or push the sensor into engagement with the flange. It is also preferable that the holding system does not apply or is incapable of applying radial loads on the sensor in excess of the sensor""s capability to take such loads, thereby reducing the likelihood that the sensor housing and clamping mechanism will create distortions within the body of the sensor that degrade its performance.
Through this use, in the present invention of a combination of a flange and holding system, the housings can be designed to exert less force on the sensor as the combination of both the flange and clamp enhances the stability and the sensor within the housing without the need for the higher holding forces commonly used with known prior art devices.
The size of such mating flanges and therefore, the size of the housing is usually determined by the sensor size and type. However, it is preferable to keep the flange and clamping system as small as practical to allow the greatest flexibility of placement of the sensor.
The depth of the flange position within the receiving housing, and the relative axial position of the flange along the body of the sensor are toleranced such that when an existing sensor is removed, and the existing sensor replaced by the insertion of another sensor, the replacement sensor exhibits an insertion depth identical to the first (replaced) sensor. This continuity of insertion depths between sensors permits calibration and zero point referencing to be performed outside of the gauge or equipment where the sensor is being utilized, thus reducing the down time of the gauge or equipment during sensor change.